The use of zeolite-containing cracking catalysts has been described. The invention pertains to improvements in such zeolitic cracking catalyst to accommodate problems which inhere in current refinery trends.
Current worldwide refinery trends indicate a continuing need to process heavier feedstocks. As a result, many refiners are processing feeds containing atmospheric and/or vacuum resid fractions with high metals content. The development of a highly metals resistant cracking catalyst such as herein disclosed would reduce cracking catalyst requirements; permit the processing of heavier feeds including resids and give the refiner greater overall flexibility in unit operating conditions. The problem of metal contaminated feeds is treated in U.S. Pat. Nos. 4,158,621 and 4,645,589.
The magnitude of the problem of cracking metals-laden feeds for FCC is known. Indeed, it is evident that activity losses due to vanadium poisoning are due to destructive interaction of vanadium species and the active zeolite. Therefore, an effective trap for vanadium may be expected to significantly increase the life of FCC catalysts when processing heavier feeds. FCC catalyst requirements as high as 0.5-1.0 lbs. per barrel of FCC feed are typical when processing resids compared with 0.1-0.2 lb. of catalyst per barrel for conventional gas oils. This dramatic increase in catalyst usage is largely due to the higher metals content of the heavier resid feeds. The deleterious effects of metals have been discussed extensively in the literature (U.S. Pat. Nos. 4,376,696; 4,513,093; 4,515,900) and are also well known to those skilled in the art. Vanadium is known to substantially deactivate cracking catalysts by irreversibly destroying the active zeolite while nickel, iron and copper promote dehydrogenation reactions which result in increased coke and dry gas yields at the expense of the desired liquid products. On the other hand, sodium reduces catalyst activity by neutralizing acid sites.